# Principles of Multicopter Flight

Alfred Gates

© Alfred A. Gates, 2014

# Principles of Multicopter Flight and

Multicopter Components

• Multicopter components



# • How a multicopter is controlled

• Myths about autopilots

• Flight in winds

• Lithium Polymer batteries

• Electronic speed controllers



# • Brushless motors

© Alfred A. Gates, 2014Autopilot Receiver Electronic Speed Controller

GPS

- Compass, battery and transmitter not displayedBrushless Motors

GPS Compass in top cover

© Alfred A. Gates, 2014© Alfred A. Gates, 2013

- 2014 5 Pilot: moves stick forward Controller move aircraft forwards and minimizes change in ROLL or YAW movements, rate of change with the MEMS Gyros.© Alfred A. Gates, 2013

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Minimum Amount of Control for a Multicopter

MEMS (micro electromechanical systems) accelerometer Vibrating Structure Gyroscope The Gyroscope can detect movement on an axis and send an electrical signal Hands off hovering a multicopter in rate mode The controller will detect a rate/rotation about an axis and correct it to a point. It will drift.

Flying a multicopter manually. The pilot sends a command to the multicopter to move forward. The controller interprets the command with the MEMS gyro and executes the command.

The correction response can be adjusted with the Gyro Gains.© Alfred A. Gates, 2013

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Movement: Increase in altitude, Vertical Position Control Method of Movement: Thrust

Increase or Decrease RPM Increase or Decrease RPM© Alfred A. Gates, 2013

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Movement: Rotate about a vertical axis, Yaw Control

Increase RPM Decrease RPM

Method of Movement: Differential Torque© Alfred A. Gates, 2013

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Movement: Forward Flight, Pitch Control Method of Movement: Differential thrust

Increase RPM Decrease RPM© Alfred A. Gates, 2013

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Movement: Sideways Flight, Roll Control Method of Movement: Differential thrust

Increase RPM Decrease RPM© Alfred A. Gates, 2013

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## Autonomous Control of a Multicopter

Additional Components IMU MEMS Gyros, 3 Axis Accelerometers, 3 Axis Magnetometers, 3 Axis Barometric Pressure, 1 Axis

GPS: Latitude, Longitude and Altitude position sensor Magnetometer: Heading sensor Autopilot Software:

# Myths About Autopilots

• Autopilots will fly any aircraft

– The autopilot gains must be adjusted to fly each different aircraft.

• Once the gains are set in an autopilot it will fly the aircraft in any condition

– Autopilots are tuned to fly aircraft in calm conditions and levels of windy conditions.

• Once the gains are set in an autopilot for calm condition the autopilot can fly the aircraft

– A tuned aircraft may not be able to recover from a stall or spin or other maneuvers.

– Each aircraft must undergo a series of test to verify the autonomous flight capabilities.

• Once an aircraft has successfully completed the flight testing and tuning the autopilot will be capable of flying it

– Other factors can interfere with an autopilot. They included, aircraft wear, to much free movement of control linkage, flexible airframe, poor GPS signal, moving ESCs or wiring, antennas to a new locations (EMF interference), replacing components on installing new components in the aircraft. (Additional factors not listed)

• A properly tuned aircraft can be flown on a new mission once the power plant is turned on and running

– The aircraft must undergo a preflight inspection followed by in flight verification testing before the autopilot can be switched to autonomous flight

© Alfred A. Gates, 2013

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# Multicopter

• Flight limitations in GPS hold it can’t fly as well in ATT mode due to max allowed bank. Important 

# to know this in winds (20MPH). The multicopter may not be able to hold position in GPS mode. In ATT mode an experience pilot could hold position in winds.



# • ATT mode best for flight in winds (20MPH)

• The best flight mode for high winds will be manual mode since the max bank it the highest and the throttle response is the highest to change 

# altitude. An experience pilot is required.

# Lipo Batteries

- ESCs

- Motors

• Max Lipo battery capability 

# must be greater than motor capability

• Max ESC current draw capability must be greater than motor capability. ESC also must be able to handle the number of battery cells

• If not the battery and or ESC will be destroyed

# Lithium Polymer, Lipo , Battery Technology

• Lipo batteries must be stored in a cool 

# location

• In hot weather store the batteries is a cooler

• In freezing weather Lipo batteries will be damaged if frozen

• If the batteries are not used for an extended time store them at a half charged setting

• Store the batteries in a battery burn proof bag

# Lipo Batteries

• Must be charged with a Lipo charger.

• Minimum loaded voltage (aircraft is in flight) must not go below 3.2V/ cell. The battery will be damaged below 3.2V/cell. Use 3.4V/cell as a minimum.



### • Minimum unloaded voltage must not go below 3.7V/cell. The battery will be damaged over time.

• Over time a battery pack will become puffy and the operating time will decrease

• ESC are programed to cut power to the motor at 3.2V/ cell for fixed 

### wing aircraft.

• Must be disconnected from circuit when not used.

• They can explode if shorted out. They will definitely catch on fire.

• Discharge battery before throwing it out pr. manufacture recommendations.

Alfred A. Gates, Ph.D.,P.E., © 16

# Lipo Batteries

New highest flight time Lipo battery Damaged puffy Lipo batteryCharging lead Aircraft power source and chargingSet number of cells Set the amperage

2 cells or 7.4V 4200mahr or 4.2A

This should be in a battery bag. If the battery puffs up stop charging immediately



## Lipo Battery Charging

# Lipo Battery Terminology

Power for 1 hour 5.0 Amps X 3 Cells X 3.7Volts/cell = 55.5 Watts for one hr Amperage for 1hr of use Number of cells and voltage Max continuous discharge amperage Max burst amperage

# Lipo Battery Terminology

Max continuous power 5.0 Amps 35C X 3 Cells X 3.7Volts/cell = 1,942.5 Watts = 2.6 hp Time for 2.6hp output = 5 Amps/ (5Amps X 35C) = .14 hr X 60min/ hr = 8.6 min Amperage for 1hr of use Number of cells and voltage Max continuous discharge amperage Max burst amperage

# Lipo Battery Terminology

Max continuous power ( This can only occur for a few seconds) 5.0 Amps 70C X 3 Cells X 3.7Volts/cell = 3,885 Watts = 5.2 hp Amperage for 1hr of use Number of cells and voltage Max continuous discharge amperage Max burst amperageAlfred A. Gates, Ph.D.,P.E., © 26 1800 Mah X 1A/1000Ma X 11.1V = 20 Watt hr This battery can produce 20 Watts for 1 hr

C rating the battery can produce 30 times the amperage or power 30C X 1800Mah X 1A/1000Ma = 54 Amps

How long will this battery last at discharge rate of 54 Amps

(1800 Mah X1A/1000Ma) /54Amps = .033hr X 60min/hr = 2 min

3S battery pack (3 cells at 3.7Volts/ cell) = 11.1 volts

Power output for 2 min = 54Amps X 11.1 Volts = 599. Watts (.8hp) 

# Example 2

# Electronic Speed Controller

# Brushless Motors Basics

• Motor max current capability must be less than ESC 

# max current capability

• Motor max current capability must be less than max Lipo battery current discharge

• High KV rating = Low Torque and High RPM

– High speed flight, slow acceleration

– ( Use smaller diameter and pitch props)



## • Low KV rating = High Torque and Low RPM

– Low speed flight heavy lifting (Multicopters)

– Higher acceleration

– (Use larger diameter and pitch props)

Alfred A. Gates, Ph.D.,P.E., © 28

# Brushless Motors Basics

• Motor efficiency: The percent efficiency goes 

# into power to the propeller. The remainder goes into generating heat.

• Example 85% efficiency, 85% power goes to 

# the propeller thrust, 15% power goes into generating heat. If the motor is large and the power demand is high the soldered wires could be melted.



# • Always go with high efficiency.

Alfred A. Gates, Ph.D.,P.E., © 29Max Current Draw From Motor < ESC and < Battery

Max current draw from motor is 20A

Max continuous current is 25A

Max continuous current 1.8A X 30C = 54A 950KV X 11.1V = 10545 RMP

Alfred A. Gates, Ph.D.,P.E., © 30

Acceptable/no firesExample 3 RPM Estimation from KV, High Torque

Alfred A. Gates, Ph.D.,P.E., © 31 360KV * 3.7V/Cell * 6S/Cell = 7,992 RPM Put a big propeller on this (15 inch)

Max thrust 2080 grams (4.6 Lb ) 14.7Amps, 6S Lipo Propeller size 15 inchesAlfred A. Gates, Ph.D.,P.E., © 32 • Max power 14.7 A X 3.7V/Cell * 6S/ Cell = 14.7A * 22.2V = 326.4W

• 326.4W X 6 motors in a Hexcopter = 1951 W ( 2.6 Hp )

• Use a 5000mah 6S batteries

• Flight time = (Battery amps pr hr)5000mah /(14.7A *6)* 60min/hr = 3.4 min

• Lifting capability = 2080g X 6 motors /454 g/Lb = 27Lb for 3.4 min

• 27 pounds for 3.4 min